A known vehicle drive unit that includes an engine with an attached axial gap type rotating electric machine is disclosed in JP-A-20060271040. The disclosed vehicle drive unit is provided with a crank case, a crank shaft that is driven to rotate around a center axis by a piston within the crank case, and an axial gap type rotating electric machine that is operatively connected via a belt-type continuously variable transmission to one end of the crank shaft within the crank case.
The axial gap type rotating electric machine is disposed in parallel to the crank shaft. The electric machine is provided with a rotating shaft that has one end that is linked to the belt-type continuously variable transmission, a rotor that is fixed to the other end of the rotating shaft, and a stator that is fixed to the crank case at a position further toward the other end than the rotor, with the rotating shaft inserted therethrough.
A plurality of permanent magnets is disposed orthogonal to the axial center of the rotating shaft in a surface of the rotor that faces the stator. The stator has a magnetic flux generating area that faces each permanent magnet in the axial direction.
More specifically, the stator includes a first stator that has first teeth that form the magnetic flux generating area, and a second stator that has second teeth that rotate relative to the first teeth around the axial center. The second stator has a structure that allows a gap, which generates magnetic resistance, between the second teeth and the first teeth to be varied.
The first stator is fixed to the crank case, and the second stator is provided with a drive mechanism that causes the second stator to rotate relative to the first stator.
The above-described vehicle drive unit is mounted in a straddle-type vehicle, most typically a motorcycle. Furthermore, the attached axial gap type rotating electric machine of the vehicle drive unit, which can be operated as a generator, can also be used to drive the driving wheel of the straddle-type vehicle. In one case, the axial gap type rotating electric machine may provide an auxiliary drive force to the drive force provided by the crank shaft that is driven to rotate around the axial center by the piston. In another case, the driving wheel of the straddle-type vehicle may be driven only by the axial gap type rotating electric machine.
In the above-described vehicle drive unit, a drive mechanism rotates the second stator, thereby changing the gap that generates the magnetic resistance between the first teeth and the second teeth. As a result, the relationship of the rotational speed and the rotational torque can be controlled. Accordingly, the output characteristics of the axial gap type rotating electric machine can be changed in accordance with the running state of the straddle-type vehicle. For example, the output characteristics can be changed to a high torque low speed mode or a low torque high speed mode.
However, in the above-described vehicle drive unit comprising an engine with an attached axial gap type rotating electric machine, the axial gap type rotating electric machine is operatively connected to the crank shaft of the engine via a belt-type continuously variable transmission, which makes reducing the size of the engine with the attached axial gap type rotating electric machine difficult. As a result, the above-described vehicle drive unit is more difficult to mount in the straddle-type vehicle, etc.
The invention has been devised in light of the above-described circumstances, and it is an object thereof to provide a vehicle drive unit comprising an engine with an attached axial gap type rotating electric machine that is easier to mount in a straddle-type vehicle.